What is Yanmar General Fault Code U0167?

Fault Code U0167 indicates a lost communication error between the Engine Control Module (ECM) and the Vehicle Immobilizer System or Security Control Module. This is a CAN bus (Controller Area Network) communication fault specific to Yanmar excavators equipped with anti-theft or immobilizer systems.

This diagnostic trouble code (DTC) triggers when the ECM cannot receive or verify signals from the immobilizer module within a specified timeframe. In Yanmar equipment, this communication pathway is essential for authorizing engine startup and maintaining proper machine operation. The CAN bus network serves as the digital nervous system of modern excavators, and any disruption in this communication chain can prevent normal operation or cause unexpected shutdowns. For used excavators, this code often emerges due to degraded wiring, corroded connectors, or module failures related to age and environmental exposure.

Common Symptoms

• Engine cranks but fails to start or starts briefly then shuts down immediately
• Immobilizer warning light remains illuminated or flashes on the instrument panel
• Security system malfunction indicator appears on the display screen
• Intermittent starting issues, particularly after the machine sits unused for extended periods
• Complete loss of communication with diagnostic tools when attempting ECM access

Potential Causes

The most frequent causes of U0167 in used Yanmar excavators include:

• Corroded or damaged connectors at the immobilizer module or ECM harness connections (common in machines exposed to moisture)
• CAN bus wiring damage from cable chafing at pivot points near the operator cab or engine compartment
• Failed immobilizer control module due to age, water intrusion, or internal circuit board deterioration
• Low battery voltage or weak batteries causing insufficient power for module communication
• ECM software corruption or version mismatch after previous repairs or component replacements
• Aftermarket key or transponder issues in machines with replaced ignition systems

How to Troubleshoot and Fix Code U0167

Step 1: Verify Power Supply and Battery Condition Check battery voltage with a multimeter—it should read 12.5-13V minimum with the key off. Inspect all ground connections at the ECM and immobilizer module for corrosion or looseness. Low voltage is a common culprit in used equipment.

Step 2: Inspect CAN Bus Wiring and Connectors Physically examine the wiring harness between the ECM and immobilizer module. Focus on known rub points near the cab mounting area and engine firewall. Look for frayed wires, damaged insulation, or green corrosion on connector pins. Clean all connections with electrical contact cleaner.

Step 3: Test CAN Bus Communication Using Yanmar diagnostic software or a compatible scan tool, check for additional communication codes. Measure CAN High and CAN Low resistance—you should see approximately 60 ohms between the two lines with all modules connected. Values outside 55-65 ohms indicate wiring faults or module failures.

Step 4: Verify Immobilizer Module Function If wiring checks pass, test the immobilizer module by swapping with a known-good unit if available. For used excavators, these modules often fail internally. Ensure the transponder key is original to the machine—aftermarket keys may not communicate properly.

Step 5: Check for ECM Software Updates Contact a Yanmar dealer to verify the ECM firmware version. Older software may have known communication bugs that updates can resolve.

Disclaimer: This guide provides general troubleshooting information. Complex electrical diagnostics should be performed by qualified technicians with proper training and equipment. Always consult official Yanmar service documentation and consider professional diagnostic services for persistent issues.